The present invention relates to a charged particle beam apparatus adapted to measure, observe and/or inspect a fine pattern formed on a sample and an image forming method used in the charged particle beam apparatus.
In a charged particle beam measurement apparatus which is represented by a scanning electron microscope, a scintillator and a photomultiplier tube are used in combination in order to detect secondary electrons and back scattered electrons which are generated when the sample has been irradiated with electron beams. When light emitted from the scintillator is incident upon the photomultiplier tube, a photoelectron is emitted from a photoelectric surface and the photoelectron is multiplied by the photomultiplier tube. Here, since a pulse interval between pulses of a signal output from the photomultiplier tube is narrow in a region where the incident light is intense, the signal exhibits an analog waveform that the pulses are mutually superimposed. However, when the light becomes faint, the signal exhibits a pulsed output waveform that the pulses are individually discrete.
As related art pertaining to a system of detecting the analog waveform and the pulsed output waveform as described above, there is a technology described in Japanese Patent Application Laid-Open No. 2011-175811 (Patent Literature 1).
In Japanese Patent Application Laid-Open No. 2011-175811 (Patent Literature 1), the following content is described. That is, there is described a charged particle beam apparatus which includes a decision unit which decides whether an output signal is an output signal which is in a state where one charged particle is incident upon a detector concerned or an output signal which is in a state where a plurality of the charged particles are incident upon the detector concerned, and an arithmetic operation unit which performs image formation by signal processing using a pulse counting method when it has been decided that the output signal is the output signal which is in the state where one charged particle is incident upon the detector concerned and performs image formation by signal processing using an analog method when it has been decided that the output signal is the output signal which is in the state where the plurality of charged particles are incident upon the detector concerned.